Torque arms have been used to connect a first rotatable body (driven, for example, by a motor) to a second concentric rotatable body (driven by the first rotatable body), both rotating about a common axis of rotation. For example, referring to FIG. 1, a torque arm 130 connects a first hollow cylindrical rotatable body 120 (such as a hollow drum driven by a motor) to a second concentric rotatable body 110, (such as a body surrounded first rotatable body). Second rotatable body 120 is driven by first rotatable body 110 via torque arm 130. First and second rotatable bodies are separated by a radial distance 140. Torque arm 130 may take the form of a threaded, rigid bar (i.e. a torque bar) having a length substantially equal to radial distance 140. First rotatable body 110 rotates about an axis 115, running perpendicular to the plane of the paper of FIG. 1. Similarly, second rotatable body 120 rotates about an axis 125 running perpendicular to the plane of the paper of FIG. 1. Ideally, axes 115, 125 coincide such that both bodies 110, 120 rotate about a common axis of rotation 125. Under ideal conditions, second rotatable body 120 rotates with the same angular velocity as that of first rotatable body 110, about the common axis 125 of rotation. As a result, a given point on first rotatable body 110, for example, point 117 and a given point on second rotatable body 120, for example, point 127 are always linearly aligned along a given diameter of first rotatable body 110, during the rotations of first and second rotatable bodies 110, 120. Thus, a position encoder may be disposed on second rotatable body 120 to determine the angular orientation of first rotatable body 110 relative to axis 125 of rotation.
However, during the rotation of first and second rotatable bodies 110, 120, radial distance 140 therebetween may vary because of component run-outs and/or variations in the axes 115, 125 of rotations of bodies 110, 120. As is known in the art, component run-out refers to the variation in the radial distance of a given point on an outer surface of a rotating component relative to the axis of rotation, due to, for example, an imbalance of material of the rotating body on one side as compared to the other side, as the component is rotated through a 360° rotation. Torque bars 130 are, therefore, subject to deflection and/or bending due to variations in the radial distance (represented by reference number 140) between first and second rotating bodies 110, 120. One such variation in radial distance 140 due to a variation in axis 125 (e.g. represented by reference numeral 125) from the common axis 125 of rotation of second rotatable body 120 and the resulting bending of torque bar 130 are schematically illustrated in broken lines (130, 130) in FIG. 1. Bending and/or deflection of torque bar 130 may result in a misalignment between first and second rotatable bodies 110, 120 (as represented by non-linear orientation of point 117 on first rotatable body and point 127 on second rotatable body relative to a diameter of first rotating body 110. Such misalignment between first and second rotatable bodies 110, 120 renders the positional measurements of an encoder disposed on second rotatable body 120 inaccurate and unreliable.
One example where such a torque bar may be used is a radar system wherein a radar antenna is mounted on a rotatable platform. The rotatable platform is configured to continuously rotate (e.g. via a drive motor assembly) about a central axis through three hundred and sixty degrees of rotation. As is known in the art, such a radar antenna uses an electromechanical connection, which is most often referred to as a′slip ring, to transmit electrical signals between a stationary structure (such as a grounding connection) to the rotatable platform which includes the radar antenna. As is known in the art, a slip ring has a rotatable component generally tracking the rotatable platform and a stationary component in at least electrical communication with the rotatable component. Radar slip rings may further include a position or azimuth encoder to determine the relative angle of the rotatable component (and thereby that of the rotatable platform) with respect to the stationary component of the slip ring and ultimately determine the angular orientation of the rotatable radar antenna.
Under ideal conditions, the rotatable component of the radar slip-ring and the rotatable platform would have the same or consistent angular bearing relative to the stationary component of the radar slip-ring. A signal generating component of the encoder may, therefore, be mounted on the rotatable component of the slip ring and a reference component of the encoder may be mounted on the stationary component of the slip ring. However, the variations in the axes of rotation of the rotating platform and the rotating component of the slip ring and component run-outs of these rotatable parts may cause undesirable bending and/or deflection of a conventional torque bar connecting the rotatable component of the slip ring and the rotatable platform of the radar, as described above. Such undesirable bending may introduce positional or angular misalignment between the rotating platform and the rotating component of the slip-ring, thereby rendering the positional measurements of the encoder generally unreliable and inaccurate. This, in turn, may adversely affect the performance of the rotatable radar antenna. Alternatives to conventional threaded, rigid torque bars are, therefore, desirable for mitigating these adverse effects on positional accuracy measurements.